Variable with json type is not stored

Hello, I have a Camunda 7.15.0. I’m trying to save object with json type into variables by using this example:, but variable with json type isn’t created. If I change type to another like String or whatever, variable will be created and storing, but I need json type to interact with variable during working with diagram.

test_json_variables.bpmn (3.2 KB)

html code

<form role="form" class="form-horizontal">
    <script cam-script type="text/form-script">

        var customer = $scope.customer = {};
      camForm.on('form-loaded', function () {
        // declare a 'json' variable 'customer'
          name: 'customer',
          type: 'json',
          value: customer
    <div class="control-group">
        <label class="control-label" for="firstName">First Name</label>
        <div class="controls">
            <input id="firstName" class="form-control" type="text" ng-model="customer.firstName" required />